Pianos, also called pianofortes, within the meaning of the invention, comprise the whole of those stringed instruments in which clamped strings are struck by means of a keyboard (fingerboard) via so-called hammers and are thereby caused to vibrate and to emit sounds. In this context, pianos are divided in particular into two groups, on the one hand, the so-called pianino in which the strings are clamped in and run vertically, on the other hand the grand pianos in which the strings are arranged in a horizontal alignment.
As mentioned before, in the case of such pianos, the strings typically clamped in a frame are struck by a so-called piano hammer that, due to a keystroke on the keyboard, hits the string or, respectively, the several strings (in the case of high tones, frequently two or more strings are clamped in parallel) in order to cause them to vibrate. To this end, the piano hammer is integrated into a complicated mechanism that, in addition to the hammer striking the string, also serves other elements, for example sound attenuation. The piano hammer per se comprises a hammer handle and a hammer head, with the latter actually impacting the string to be struck or, respectively, the strings to be struck, upon actuation. The core of the hammer head of a piano hammer, like the hammer handle, is frequently made of wood but is not necessarily limited to this material. In this context, the core of the hammer head is provided with a cover with which the hammer head will impact the strings to be struck when the corresponding key of the keyboard is activated. Nowadays, felt is usually used as material for the cover, but leather has also been used before. Other materials with comparable properties are conceivable for use as cover as well.
In the case of known pianos, the hammer or, respectively, the hammer cover is typically designed in the shape of a drop with a strike area with which it impacts the string or, respectively, the strings when the corresponding key is activated. In this context, for example in the case of the use of felt for the cover of the hammer head, as is quite common today, the density or, respectively, the compression of the felt plays an essential role with regard to the sound properties or, respectively, the intonation of the instrument when the hammer is activated. For example, during the manufacture of pianos at the factory, the felt covers of the hammers are loosened in the areas with which they impact the string or, respectively, the strings for an acoustic tuning by piercing their surface with certain tools, thereby conditioning the felt. This work must be performed by experienced tuning personnel and is time consuming. In particular, it will be hardly possible to recompress a piano hammer treated by the process described above whose cover, in particular a felt cover, has been loosened too much by means of the aforementioned piercing. In the worst case, the hammerhead, or even the entire hammer, will have to be replaced while still in the production process and the tuning must be performed anew.